The present invention relates to aluminum extrusion, and more particularly to the process of cutting billets from aluminum logs exiting a furnace.
Aluminum extrusion is a well known and widely practiced technology. Aluminum logs are heated within a log furnace to a temperature suitable for extrusion. As each log exit the furnace, billets are cut from the log and transferred to an extrusion press. With the press, the billet is extruded through a die to create an article having a desired shape and length. The total length of the extruded shape is a multiple of the length of the pieces to be cut from the shape plus process scrap. The required billet length is directly proportional to the desired extrusion length.
Cutting billets of desired lengths from a heated aluminum log creates remainders or off-cuts. One challenge in aluminum extrusion is to use the remainders or off-cuts without resorting to recycling or re-melting due to the inherent costs involved. The preferred method for the use of remainders or off-cuts is to combine them with another log segment (known as a “short-cut piece”) to create a two-piece billet. The two-piece billet is loaded into the press container, and the two pieces fuse together as the abutting faces of the two pieces pass through the extrusion die. Unfortunately, the spaces and gaps between the two pieces entrap air that produces unacceptable blisters in the finished product. Furthermore, the oxide film on the two abutting faces of the two-piece billet produces defective or unsound fusions or welds between the faces as the aluminum moves through the extrusion die.
One prior art attempt has been made to create an effectively “continuous” log as input to the furnace. Specifically, sequential logs are attached together in end-to-end fashion as the logs are moved into the furnace. The attachment is created by “friction stir welding” or surface welding the abutting logs. This technique has at least two problems. First, the ends of the logs are rarely square; and the logs are rarely straight. Consequently, the connected logs result in a log column that is non-linear (i.e. snake-like). The log column does not lay evenly on the supporting rollers; and the log column is difficult to move through the furnace. Second, this technique does not resolve the above noted problems of entrapped air and oxide.